THz radiation, the high frequency end of the microwave (MW) band, is presently believed to be a potential candidate for future short distance high speed wireless connections, e.g. as a replacement for Bluetooth technology. Other interesting applications are in lab-on-a-chip applications as well as in all optical computing.
Typically, THz radiation is formed and applied as pulsed radiation, often generated from ultrashort laser pulses, hence, THz pulses are often in the picosecond (ps) or sub-picosecond (subps) range.
For this reason, pulse broadening due to group-velocity-dispersion (GVD) plays an important role when trying to propagate THz pulses in waveguides.
Parallel plate waveguides (PPWG) have been shown to induce only little pulse broadening and furthermore providing efficient quasi-optic coupling of freely propagating THz pulses, see e.g. “Undistorted guided-wave propagation of subpicosecond THz pulses”, Mendis et. al, Opt. Lett. 26, 846 (2001).
For the purpose of controlling THz pulses in PPWGs, integration of various components have been suggested, such as a photonic waveguide stop bands and transmission bands, see “THz parallel plate photonic waveguides”, Bingham et. al, Appl. Phys. Lett. 87, 051101 (2005) and references therein.
A metal waveguide that can be used in a THz laser or amplifier is described in US patent application No. 2005/058166.
The implicit simplicity of the structure of PPWGs makes them suitable for integration on integrated circuits and MEMS devices, such as chips and structures based on silicon and photolithography technology. Hence, ways of controlling THz radiation in PPWGs would be advantageous, and in particular ways that also allow such integration would be advantageous.
JP 2006071801 relates to coupling of THz radiation in/out of a THz waveguide. Photo-induced free carriers are induced in a semiconductor slab waveguide based on total internal reflection in a Si layer sandwiched by quartz and air, possibly with a microstrip transmission line. The induced free carriers serves to couple THz in/out of the waveguide or to absorb the radiation.
Also, the high frequency (as compared to electrical signals) and ultrashort nature of THz pulses makes them if interest to high speed data transmission, and therefore active components that can be used for this purpose would be advantageous.